Expression of milk protein genes in the lactating mammary gland is controlled by steroid and peptide hormones. The thrust of work is toward and understanding of the cis-element(s) and trans-acting factor(s) that determine tissue specificity and hormone inducibility of the gene for the whey acidic protein (WAP). Studies on the interaction of nuclear proteins from mammary epithelial cells with the WAP gene promoter region revealed that the region between -10 and -200 is recognized specifically by at least four different proteins. In order to elucidate the functional significance of those potential trans-acting factors we need to develop in vivo assays. In collaboration with Dr. Bernd Groner's laboratory (Bern, Switzerland) transgenomic mice were established that carried the Harvey-ras gene under the control of the WAP promoter. The fusion gene was expressed only in the lactating mammary gland. This indicates that the promoter fragment contained the regulatory elements necessary for controlled expression. Furthermore the female mice developed mammary tumors and therefore can be used to study mammary tumorigenesis. These studies demonstrate for the first time a sequence specific binding of nuclear proteins to a mammary specific promoter and tissue specific expression of this promoter in transgenomic mice. In the second project we investigate cellular factors necessary to activate human cytomegalovirus, a known pathogen. We started experiments to define in vivo and in vitro activator and repressor elements that govern the expression of the first gene within the viral lifecycle. In collaboration with Dr. Fleckenstein's laboratory we defined sites of protein-DNA interaction in an enhancer and potential repressor element.